In measuring angular velocity, the principle of the method of measuring based on a vibrating sensor of angular velocity has proved to be simple and reliable. In a vibrating sensor of angular velocity, a certain known primary motion is induced and maintained in the sensor. The desired motion to be measured by means of the sensor is then detected as a deviation of the primary motion.
An external angular velocity in a direction perpendicular to the resonators' direction of motion acting on the sensor induces a Coriolis force in the seismic mass in a direction perpendicular to its direction of motion. The Coriolis force, proportional to the angular velocity, is detected, for example capacitively, in the vibration of the mass.
One of the most significant problems in micromechanical vibrating sensors of angular velocity is the so called quadrature signal, which is caused by poor dimensional precision in the structures. In resonators manufactured using the means of micromechanics, there may be found tolerance errors in the perpendicularity of the directions of motion, which in the detection of the sensor of angular velocity cause a signal, called the quadrature signal, of a magnitude, at worst, hundreds of times larger than the angular velocity signal corresponding to the maximum value of the output scale.
The angular velocity signal to be measured, being proportional to the speed of the mass, is luckily phase-shifted by 90 degrees in relation to the quadrature signal, whereby the quadrature signal disappears in an ideal demodulation. However, being significantly larger than the signal to be measured, it restricts the dynamics of the signal. Another big disadvantage of the quadrature signal is, that it, if left uncompensated for, significantly degrades the stability of the zero point of the sensor, due to phase shifts in the electronic signals as, for example, the temperature changes.
In the sensor, the quadrature signal can be compensated for by using electric forces. One of the known techniques is i.a. feed-forward compensation, in which a force modulated by the detected primary motion is fed back into the detecting resonator at a phase opposite to the quadrature signal. Alternative ways of electrical compensation include, for example, straightening of the direction of motion by a static electric force or by a force generated by a static entity modulated by the motion, which force compensates for the quadrature signal caused by a residual of the spring force.
Compensation by means of electric forces constitutes a challenge to the sensor's electronics. What is required is either accurate phase control or, possibly, large voltages and separate structures within the sensor.
Thus, the object of the invention is to provide a structure of a vibrating sensor of angular velocity, in which the compensation for the quadrature signal is implemented directly by mechanical design, without electric forces.
Referring to prior art, the Finnish patent publication FI-116543B1 describes a sensor of angular velocity according to prior art, where the seismic masses are connected to support areas by springs and/or stiff auxiliary structures, which give the masses a degree of freedom in relation to an axis of rotation perpendicular to the plane of the disk they are forming, and to at least one axis of rotation extending in the direction of the plane of the disk.
Further, referring to prior art, the Finnish patent publication FI-116544B1 describes a sensor of angular velocity according to prior art, where at least one pair of electrodes is formed in association with the edge of the seismic mass, which pair of electrodes forms two capacitances with the surface of the mass, so that, as a function of the angle of rotation of the mass's primary motion, one capacitance of the pair of electrodes increases and the other capacitance of the pair of electrodes decreases.